As a spatial position detection apparatus, there is exemplified a three-dimensional position detection apparatus which forms images based on infrared rays radiated from a human body by using plural infrared cameras and calculates center coordinates of the human body based on the detected images to detect a position of the human body (JP 07-035842 A). In addition, another spatial position detection apparatus is known in which a beam is emitted from a LED and based on an electromagnetic wave reflected by an object, an angle and intensity of a reflected light are calculated to thereby detect a position of the object (JP 08-082670 A).
Common information input apparatuses utilizing an electromagnetic wave include a touch panel and a pen input apparatus. For example, there is a pen input apparatus which calculates information on incident angles of lights emitted from a pen tip and entering light receiving elements (each of which is composed of a CCD and a lens) installed in two positions, based on irradiation position information of the lights incident on surfaces of CCDs, thus detecting a position of the pen tip (JP 06-168065 A).
In the above-mentioned spatial position detection apparatus utilizing infrared rays, a three-dimensional image of the object is constructed based on images taken by the plural infrared camera. However, if each of the infrared images formed using the infrared cameras does not include information on an angle to some extent, it is difficult to construct the three-dimensional image of the object. To allow each of the infrared images to include angle information, the necessity arises to arrange the infrared cameras spatially, which leads to a problem of making the apparatus structure large. In the apparatus for detecting the position of the object based on the light reflected by the angle and the intensity of the reflected light by using the LED as described above, a light source driver device needs to be provided separately, and therefore the apparatus also has a problem in that its structure becomes large.
In the aforementioned pen input apparatus, the lights are emitted from the pen tip to detect a position of the pen tip based on information on the incident angles of the lights entering the light receiving elements. However, for the pen input apparatus, it is at least necessary to secure a space for disposing the light receiving elements in front of the interface section. Moreover, in this case, since light has a rectilinear characteristic, there is a problem with flexibility in layout. For example, it is difficult to arrange the light receiving elements for detecting the object position in an interface section having irregularities or a curved surface.